Proceedings Paper

Twenty-three years ago G. E. Pugh and then later Leonard Schiff independently suggested the possibility of performing two new tests of Einstein's General Theory of Relativity by observations on orbiting gyroscopes. The experiment calls for the development of a free precession gyroscope with drift-rates less than 10-11 deg/hour, many orders of magnitude below the performance of typical inertial navigation instruments. A team of physicists and engineers at Stanford University have developed under NASA support a gyroscope that appears to have the required performance characteristics making use of a combination of novel cryogenic and space physics techniques. The gyro is an electrically suspended sphere, spun up initially by means of gas jets to a speed of 200 Hz and then allowed to coast freely in a 10-9 torr vacuum. The orientation of the spin axis of the gyroscope is read out by observing the direction of the "London moment" in the rota-ting superconductor with the aid of SQUID (Superconducting QUantum Interference Device) magnetometers.